Nucleosome positioning

Genomic nucleosome positions determine DNA accessibility to regulatory molecules, and thus modulate gene expression. Nucleosome positioning can be characterised by the location of the nucleosome centres, average occupancy landscapes, the stability of individual nucleosomes, and integral parameters such as the nucleosome repeat length. Nucleosome positioning depends on the DNA sequence affinity of the histone octamer, statistical positioning of nucleosomes by genomic boundaries, chemical modifications of DNA or histones, abundance of linker histones, competitive binding of transcription factors, and nucleosome repositioning by chromatin remodellers. The quantitative description of nucleosome positioning depending on the cell type/state has been addressed using a number of approaches, and this problem still poses significant challenges.